This study is testing a new medicine called AZD7789 for people with advanced cancer. The medicine is a special type of drug called a bispecific antibody, which can target two different parts of cancer cells to help the body's immune system fight the cancer. The study is in early stages (Phase I/IIa) and will see if the medicine is safe and works well. Patients will get the medicine through an IV (a drip into the vein) and the study will have two parts to find the best dose.

Eligibility: Adults with certain lung and stomach cancers that cannot be treated with surgery or radiation can join. Participants need to have had some cancer treatments before and meet other health requirements. Women must not be pregnant and everyone must agree to use birth control.

Exclusion: People with certain genetic cancer types, unresolved side effects from past treatments, or specific health problems like certain infections cannot join. Recent surgery or other cancer treatments may also disqualify participants.

• The study involves taking AZD7789 through an IV.
• Participants need to have had previous cancer treatments.
• The study will test safety and effectiveness of the drug.